Scalacheck won't properly report the failing case - unit-testing
I've wrote the following spec
"An IP4 address" should "belong to just one class" in {
val addrs = for {
a <- Gen.choose(0, 255)
b <- Gen.choose(0, 255)
c <- Gen.choose(0, 255)
d <- Gen.choose(0, 255)
} yield s"$a.$b.$c.$d"
forAll (addrs) { ip4s =>
var c: Int = 0
if (IP4_ClassA.unapply(ip4s).isDefined) c = c + 1
if (IP4_ClassB.unapply(ip4s).isDefined) c = c + 1
if (IP4_ClassC.unapply(ip4s).isDefined) c = c + 1
if (IP4_ClassD.unapply(ip4s).isDefined) c = c + 1
if (IP4_ClassE.unapply(ip4s).isDefined) c = c + 1
c should be (1)
}
}
That is very clear in its scope.
The test passes successfully but when I force it to fail (for example by commenting out one of the if statements) then ScalaCheck correctly reports the error but the message doesn't mention correctly the actual value used to evaluate the proposition. More specifically I get:
[info] An IP4 address
[info] - should belong to just one class *** FAILED ***
[info] TestFailedException was thrown during property evaluation.
[info] Message: 0 was not equal to 1
[info] Location: (NetSpec.scala:105)
[info] Occurred when passed generated values (
[info] arg0 = "" // 4 shrinks
[info] )
where you can see arg0 = "" // 4 shrinks doesn't show the value.
I've tried to add even a simple println statement to review the cases but the output appears to be trimmed. I get something like this
192.168.0.1
189.168.
189.
1
SOLUTION
import org.scalacheck.Prop.forAllNoShrink
import org.scalatest.prop.Checkers.check
"An IP4 address" should "belong to just one class" in {
val addrs = for {
a <- Gen.choose(0, 255)
b <- Gen.choose(0, 255)
c <- Gen.choose(0, 255)
d <- Gen.choose(0, 255)
} yield s"$a.$b.$c.$d"
check {
forAllNoShrink(addrs) { ip4s =>
var c: Int = 0
if (IP4.ClassA.unapply(ip4s).isDefined) c = c + 1
if (IP4.ClassB.unapply(ip4s).isDefined) c = c + 1
if (IP4.ClassC.unapply(ip4s).isDefined) c = c + 1
if (IP4.ClassD.unapply(ip4s).isDefined) c = c + 1
if (IP4.ClassE.unapply(ip4s).isDefined) c = c + 1
c == (1)
}
}
}
This is caused by ScalaCheck's test case simplification feature. ScalaCheck just sees that your generator produces a string value. Whenever it finds a value that makes your property false, it tries to simplify that value. In your case, it simplifies it four times until it ends up with an empty string, that still makes your property false.
So this is expected, although confusing, behavior. But you can improve the situation in three different ways.
You can select another data structure to represent your IP addresses. This will make ScalaCheck able to simplify your test cases in a more intelligent way. For example, use the following generator:
val addrs = Gen.listOfN(4, Gen.choose(0,255))
Now ScalaCheck knows that your generator only produces lists of length 4, and that it only contains numbers between 0 and 255. The test case simplification process will take this into account and not create any values that couldn't have been produced by the generator from start. You can do the conversion to string inside your property instead.
A second method is to add a filter directly to your generator, which tells ScalaCheck how an IP address string should look like. This filter is used during test case simplification. Define a function that checks for valid strings and attach it to your existing generator this way:
def validIP(ip: String): Boolean = ...
val validAddrs = addrs.suchThat(validIP)
forAll(validAddrs) { ... }
The third method is to simply disable the test case simplification feature altogether by using forAllNoShrink instead of forAll:
Prop.forAllNoShrink(addrs) { ... }
I should also mention that the two first methods require ScalaCheck version >= 1.11.0 to function properly.
UPDATE:
The listOfN list length is actually not respected by the shrinker any more, due to https://github.com/rickynils/scalacheck/issues/89. Hopefully this can be fixed in a future version of ScalaCheck.
Related
Run two infinite loop at once in Ocaml
I have programmed a langton's ant and it work nice. Now I want to run 2 ant simultaneously.I have a run function how make the computation and ant's movement and it's a infinite run loop. How can I run 2 of this loop at once ? I have try to look on Thread but i'm not sure that it's the best for my case. This is some example of my code : Run function : let run(f,tab2 : t_fourmi*int array array) = f.xx := !(f.x); f.yy := !(f.y); let d = ref 0 and z = ref 0 and o = ref 0 (* 1 = de bas, 2 = de droite, 3 = de haut, 4 = de gauche *) in if tab2.(!(f.x)/5).(!(f.y)/5) = 0 then move_right(f,1,tab2); if !(f.xx) + 5 = !(f.x) then d := 4 else if !(f.xx) - 5 = !(f.x) then d := 2 else if !(f.yy) + 5 = !(f.y) then d := 1 else if !(f.yy) - 5 = !(f.y) then d := 3; while true do (* print_string "step : "; print_int !o; print_newline(); *) o := !o + 1; f.xx := !(f.x); f.yy := !(f.y); z := tab2.(!(f.x)/5).(!(f.y)/5); if !z = 0 then move_right(f,!d,tab2) else if !z = 1 then move_left(f,!d,tab2) else if !z = 2 then move_right(f,!d,tab2) else if !z = 3 then move_right(f,!d,tab2); if !(f.xx) + 5 = !(f.x) then d := 4 else if !(f.xx) - 5 = !(f.x) then d := 2 else if !(f.yy) + 5 = !(f.y) then d := 1 else if !(f.yy) - 5 = !(f.y) then d := 3; done; ;; Example of move function : let move_left(f,d,tab2 : t_fourmi*int*int array array) = (* d = direction d'ou la fourmi viens *) (* 1 = de bas, 2 = de droite, 3 = de haut, 4 = de gauche *) f.xx := !(f.x); f.yy := !(f.y); if d = 1 then f.x := !(f.x) - 5 else if d = 2 then f.y := !(f.y) - 5 else if d = 3 then f.x := !(f.x) + 5 else if d = 4 then f.y := !(f.y) + 5; if !(f.x) >= 995 then f.x := 5 else if !(f.x) <= 5 then f.x := 995; if !(f.y) >= 995 then f.y := 5 else if !(f.y) <= 5 then f.y := 995; create_fourmi(f); let n = tab2.(!(f.xx)/5).(!(f.yy)/5) in drawinv(!(f.xx),!(f.yy),n,tab2); ;; If you need more function, ask me. Thanks
If I understand your code correctly (it's unfortunately not very readable), it could be outlined as essentially: let init params = ... let step state = ... let move thing state = ... let run params thing = let state = ref (init params) in while true do let state := step state in move thing state done where I've factored init, step and move out into separate function, which should be pretty straight-forward to do. And by doing so we can replace the run function with a run_two function that can run two instances virtually at the same time, though not entirely in parallel. They won't run independently, but in synchrony, iteration by iteration: let run_two params1 thing1 params2 thing2 = let state1 = ref (init params1) in let state2 = ref (init params2) in while true do state1 := step !state1; state2 := step !state2; move !state1; move !state2; done This doesn't use any threads or other complicated concurrency primitives. It's just ordinary code organized in a way that allows composition. It also allows the init and step function to be completely pure, which makes them easy to test and reason about. You could even make the move functions pure, if you factor out the drawing.
You can use threads, though it will open a pandora box for you. You have to synchronize your ants, since probably you want them to move in the same world.
Running two ants in different threads
First of all, you have to represent each ant process as an ever-looping function of type ant -> unit, where ant is the type that describes ant's initial position, moving parameters, and so on (if you don't need this, then just use unit instead. So suppose we have a function val run : ant -> unit. Next, we need to make sure, that we do not write to the same board at the same time from different threads, so we need to create a mutex, using Mutex.create, we then need to update our run function and do Mutex.lock before updating our board, and Mutex.unlock after. Finally, we should ensure that no ants will starve for the board, and that once an ant finishes it moves it yields the control to another ant, we could do this using Thread.delay if we want our simulation to be smooth (i.e., if we want to artificially slow it down to human-observable speed). Otherwise, we can just use Thread.yield. (Note, normally threads are preempted (forced to yield) by the system, but this is done in special yield points. When we do system programming there are usually lots of yield points, but this is not our case, so we have to implement this cooperation explicitly). Finally, our updated run function is ready to be run in a thread, with Thread.createrun ant. This function will return to our main thread of execution, so we can run a second ant and so on. Once all ants start running we have to call Thread.join to wait for all of them. Ideally, this function should never return.
I hope, that the above outline provided enough information for you, and you can enjoy the coding yourself. Feel free to ask questions int the comment section if anything is unclear. Probably, the first question would be how to compile it. It is (there are simpler ways, of course, but the most basic is, assuming that your program is in the ant.ml):
ocamlopt -thread unix.cmxa threads.cmxa ant.ml -o ant
Running two ants in co-routines
While the above will work, it seems too complicated and too system-dependent for such a simple simulation task. Why do we need to use system threads for that? We actually don't, we can be clever and implement co-routines using plain OCaml and continuation-passing style. Don't worry, a continuation is just a function. And a continuation-passing style is when we are calling another function at the end of the other function. In this approach, we will not have the run function that runs infinitely, instead, we will have a step function that advances an ant one step forward at each invocation. For the demonstration purposes, let's simplify our step function so that each ant just greets another, e.g.,
let step other yield =
print_endline ("Hello, " ^ other);
yield ()
That simple. We do our step, and then call the yield function (that is that fancy continuation) to yield the control to the next ant. Now let's tie it together in a simple infinite loop, e.g.,
let rec loop () =
step "Joe" ## fun () ->
step "Doe" ## fun () ->
loop ()
let () = loop ()
Let's make it clear. step "Joe" ## fun () -> <continue> is the same as step "Joe" (fun () -> <continue>), and this (fun () -> <continue>) is the yield function that is passed to the step function that greets Joe. Once Joe is greeted the step function calls us again and we evaluate the <continue>, which is, in our case step "Doe" ## fun () -> loop (), i.e., we pass the fun () -> loop () function as the yield argument to the step function that greets Doe, so once Doe is greeted, we call loop () ... and now we're at the begining of the loop.
In our case, we were passing a value of type unit in our continuations, but we can also pass an arbitrary value, e.g., a value that will represent the state of our simulation (the board with ant positions). This will enable a functional implementation of your simulation if you want to try it.
Scala memory issue on List vs. Vector
I wrote a solution to project Euler problem #59 in Scala and I do not understand why switching between Vector and List adds what I think is a memory leak.
Here is a working, brute force solution using Vectors.
val code = scala.io.Source.fromFile("e59.txt").getLines()
.flatMap(l => l.split(',')).map(_.toInt).toVector
val commonWords = scala.io.Source.fromFile("common_words.txt").getLines().toVector
def decode(k: Int)(code: Vector[Int])(pswd: Vector[Int]): Vector[Int] = {
code.grouped(k).flatMap(cs => cs.toVector.zip(pswd).map(t => t._1 ^ t._2)).toVector
}
def scoreText(text: Vector[Int]): Int = {
if (text.contains((c: Int) => (c < 0 || c > 128))) -1
else {
val words = text.map(_.toChar).mkString.toLowerCase.split(' ')
words.length - words.diff(commonWords).length
}
}
lazy val psswds = for {
a <- (97 to 122);
b <- (97 to 122);
c <- (97 to 122)
} yield Vector(a, b, c)
val ans = psswds.toStream.map(decode(3)(code))
.map(text => (text, scoreText(text)))
.maxBy(_._2)._1.sum
println(ans)
I store original code (a collection of ordered ints), each password and some common English words as Vectors.
However, if I replace Vector with List, my program slows down with each checked password and eventually crashes:
val code = scala.io.Source.fromFile("e59.txt").getLines()
.flatMap(l => l.split(',')).map(_.toInt).toList
val commonWords = scala.io.Source.fromFile("common_words.txt").getLines().toList
def decode(k: Int)(code: List[Int])(pswd: List[Int]): List[Int] = {
println(pswd)
code.grouped(k).flatMap(cs => cs.toList.zip(pswd).map(t => t._1 ^ t._2)).toList
}
def scoreText(text: List[Int]): Int = {
if (text.contains((c: Int) => (c < 0 || c > 128))) -1
else {
val words = text.map(_.toChar).mkString.toLowerCase.split(' ')
words.length - words.diff(commonWords).length
}
}
lazy val psswds = for {
a <- (97 to 122);
b <- (97 to 122);
c <- (97 to 122)
} yield List(a, b, c)
val ans = psswds.toStream.map(decode(3)(code))
.map(text => (text, scoreText(text)))
.maxBy(_._2)._1.sum
println(ans)
Error:
java.lang.OutOfMemoryError: GC overhead limit exceeded
at java.lang.String.valueOf(String.java:2861)
at java.lang.Character.toString(Character.java:4439)
at java.lang.String.valueOf(String.java:2847)
at scala.collection.mutable.StringBuilder.append(StringBuilder.scala:200)
at scala.collection.TraversableOnce$$anonfun$addString$1.apply(TraversableOnce.scala:349)
at scala.collection.immutable.List.foreach(List.scala:381)
at scala.collection.TraversableOnce$class.addString(TraversableOnce.scala:342)
at scala.collection.AbstractTraversable.addString(Traversable.scala:104)
at scala.collection.TraversableOnce$class.mkString(TraversableOnce.scala:308)
at scala.collection.AbstractTraversable.mkString(Traversable.scala:104)
at scala.collection.TraversableOnce$class.mkString(TraversableOnce.scala:310)
at scala.collection.AbstractTraversable.mkString(Traversable.scala:104)
at scala.collection.TraversableOnce$class.mkString(TraversableOnce.scala:312)
at scala.collection.AbstractTraversable.mkString(Traversable.scala:104)
at Main$$anon$1.Main$$anon$$scoreText(e59_list.scala:14)
at Main$$anon$1$$anonfun$5.apply(e59_list.scala:26)
at Main$$anon$1$$anonfun$5.apply(e59_list.scala:26)
at scala.collection.immutable.Stream$$anonfun$map$1.apply(Stream.scala:418)
at scala.collection.immutable.Stream$$anonfun$map$1.apply(Stream.scala:418)
at scala.collection.immutable.Stream$Cons.tail(Stream.scala:1222)
at scala.collection.immutable.Stream$Cons.tail(Stream.scala:1212)
at scala.collection.immutable.Stream.foreach(Stream.scala:595)
at scala.collection.TraversableOnce$class.maxBy(TraversableOnce.scala:227)
at scala.collection.AbstractTraversable.maxBy(Traversable.scala:104)
at Main$$anon$1.<init>(e59_list.scala:27)
at Main$.main(e59_list.scala:1)
at Main.main(e59_list.scala)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at scala.reflect.internal.util.ScalaClassLoader$$anonfun$run$1.apply(ScalaClassLoader.scala:70)
Files used:
common_words.txt
a
able
about
across
after
all
almost
also
am
among
an
and
any
are
as
at
be
because
been
but
by
can
cannot
could
dear
did
do
does
either
else
ever
every
for
from
get
got
had
has
have
he
her
hers
him
his
how
however
i
if
in
into
is
it
its
just
least
let
like
likely
may
me
might
most
must
my
neither
no
nor
not
of
off
often
on
only
or
other
our
own
rather
said
say
says
she
should
since
so
some
than
that
the
their
them
then
there
these
they
this
tis
to
too
twas
us
wants
was
we
were
what
when
where
which
while
who
whom
why
will
with
would
yet
you
your
e59.txt
79,59,12,2,79,35,8,28,20,2,3,68,8,9,68,45,0,12,9,67,68,4,7,5,23,27,1,21,79,85,78,79,85,71,38,10,71,27,12,2,79,6,2,8,13,9,1,13,9,8,68,19,7,1,71,56,11,21,11,68,6,3,22,2,14,0,30,79,1,31,6,23,19,10,0,73,79,44,2,79,19,6,28,68,16,6,16,15,79,35,8,11,72,71,14,10,3,79,12,2,79,19,6,28,68,32,0,0,73,79,86,71,39,1,71,24,5,20,79,13,9,79,16,15,10,68,5,10,3,14,1,10,14,1,3,71,24,13,19,7,68,32,0,0,73,79,87,71,39,1,71,12,22,2,14,16,2,11,68,2,25,1,21,22,16,15,6,10,0,79,16,15,10,22,2,79,13,20,65,68,41,0,16,15,6,10,0,79,1,31,6,23,19,28,68,19,7,5,19,79,12,2,79,0,14,11,10,64,27,68,10,14,15,2,65,68,83,79,40,14,9,1,71,6,16,20,10,8,1,79,19,6,28,68,14,1,68,15,6,9,75,79,5,9,11,68,19,7,13,20,79,8,14,9,1,71,8,13,17,10,23,71,3,13,0,7,16,71,27,11,71,10,18,2,29,29,8,1,1,73,79,81,71,59,12,2,79,8,14,8,12,19,79,23,15,6,10,2,28,68,19,7,22,8,26,3,15,79,16,15,10,68,3,14,22,12,1,1,20,28,72,71,14,10,3,79,16,15,10,68,3,14,22,12,1,1,20,28,68,4,14,10,71,1,1,17,10,22,71,10,28,19,6,10,0,26,13,20,7,68,14,27,74,71,89,68,32,0,0,71,28,1,9,27,68,45,0,12,9,79,16,15,10,68,37,14,20,19,6,23,19,79,83,71,27,11,71,27,1,11,3,68,2,25,1,21,22,11,9,10,68,6,13,11,18,27,68,19,7,1,71,3,13,0,7,16,71,28,11,71,27,12,6,27,68,2,25,1,21,22,11,9,10,68,10,6,3,15,27,68,5,10,8,14,10,18,2,79,6,2,12,5,18,28,1,71,0,2,71,7,13,20,79,16,2,28,16,14,2,11,9,22,74,71,87,68,45,0,12,9,79,12,14,2,23,2,3,2,71,24,5,20,79,10,8,27,68,19,7,1,71,3,13,0,7,16,92,79,12,2,79,19,6,28,68,8,1,8,30,79,5,71,24,13,19,1,1,20,28,68,19,0,68,19,7,1,71,3,13,0,7,16,73,79,93,71,59,12,2,79,11,9,10,68,16,7,11,71,6,23,71,27,12,2,79,16,21,26,1,71,3,13,0,7,16,75,79,19,15,0,68,0,6,18,2,28,68,11,6,3,15,27,68,19,0,68,2,25,1,21,22,11,9,10,72,71,24,5,20,79,3,8,6,10,0,79,16,8,79,7,8,2,1,71,6,10,19,0,68,19,7,1,71,24,11,21,3,0,73,79,85,87,79,38,18,27,68,6,3,16,15,0,17,0,7,68,19,7,1,71,24,11,21,3,0,71,24,5,20,79,9,6,11,1,71,27,12,21,0,17,0,7,68,15,6,9,75,79,16,15,10,68,16,0,22,11,11,68,3,6,0,9,72,16,71,29,1,4,0,3,9,6,30,2,79,12,14,2,68,16,7,1,9,79,12,2,79,7,6,2,1,73,79,85,86,79,33,17,10,10,71,6,10,71,7,13,20,79,11,16,1,68,11,14,10,3,79,5,9,11,68,6,2,11,9,8,68,15,6,23,71,0,19,9,79,20,2,0,20,11,10,72,71,7,1,71,24,5,20,79,10,8,27,68,6,12,7,2,31,16,2,11,74,71,94,86,71,45,17,19,79,16,8,79,5,11,3,68,16,7,11,71,13,1,11,6,1,17,10,0,71,7,13,10,79,5,9,11,68,6,12,7,2,31,16,2,11,68,15,6,9,75,79,12,2,79,3,6,25,1,71,27,12,2,79,22,14,8,12,19,79,16,8,79,6,2,12,11,10,10,68,4,7,13,11,11,22,2,1,68,8,9,68,32,0,0,73,79,85,84,79,48,15,10,29,71,14,22,2,79,22,2,13,11,21,1,69,71,59,12,14,28,68,14,28,68,9,0,16,71,14,68,23,7,29,20,6,7,6,3,68,5,6,22,19,7,68,21,10,23,18,3,16,14,1,3,71,9,22,8,2,68,15,26,9,6,1,68,23,14,23,20,6,11,9,79,11,21,79,20,11,14,10,75,79,16,15,6,23,71,29,1,5,6,22,19,7,68,4,0,9,2,28,68,1,29,11,10,79,35,8,11,74,86,91,68,52,0,68,19,7,1,71,56,11,21,11,68,5,10,7,6,2,1,71,7,17,10,14,10,71,14,10,3,79,8,14,25,1,3,79,12,2,29,1,71,0,10,71,10,5,21,27,12,71,14,9,8,1,3,71,26,23,73,79,44,2,79,19,6,28,68,1,26,8,11,79,11,1,79,17,9,9,5,14,3,13,9,8,68,11,0,18,2,79,5,9,11,68,1,14,13,19,7,2,18,3,10,2,28,23,73,79,37,9,11,68,16,10,68,15,14,18,2,79,23,2,10,10,71,7,13,20,79,3,11,0,22,30,67,68,19,7,1,71,8,8,8,29,29,71,0,2,71,27,12,2,79,11,9,3,29,71,60,11,9,79,11,1,79,16,15,10,68,33,14,16,15,10,22,73
Large amount of Lists create more load on GC comparing to the same Vectors. But your problem is not about right choice of collections, but about wrong use of Stream. Scala's streams can be very memory inefficient if used improperly. In your case, I assume, you were trying to use Stream to avoid eager computation of the transformed passwds collection, but you actually made the things worse (as Stream not only memoized your elements, it created extra overhead with Stream wrappers of these elements). What you had to do is just to replace toStream with view. It will create collection wrapper which makes nearly all transformations lazy (basically what you tried to achieve). val ans = psswds.view.map(decode(3)(code)) .map(text => (text, scoreText(text))) .maxBy(_._2)._1.sum After this tiny fix you program runs fine even with -Xmx5m (I checked). There are also many other things to optimize in your program (try to avoid creating excessive collections), but I'll leave it to you.
Execute two commands in single-line If -statement
I want to execute two commands as part of a single-line If -statement: Though below snippet runs without error, variable $F_Akr_Completed is not set to 1, but the MsgBox() is displayed properly (with "F is 0"). $F_Akr_Completed = 0 $PID_Chi = Run($Command) If $F_Akr_Completed = 0 And Not ProcessExists($PID_Chi) Then $F_Akr_Completed = 1 And MsgBox(1,1,"[Info] Akron parser completed. F is " & $F_Akr_Completed) Any idea why there is no syntax-error reported when it's not functional?
There is no error, because If x = x Then x And x is a valid statement, and x And x is a logical expression. There are many ways you can do this, e.g.: If Not ($F_Akr_Completed And ProcessExists($PID_Chi)) Then $F_Akr_Completed = 1 + 0 * MsgBox(1,1,"[Info] Akron parser completed. F is " & 1) But that is a bad style of coding. AutoIt is a mostly verbose language and I recommend to seperate multiple statements. You can also assign values using the ternary operator: $F_Akr_Completed = (Not ($F_Akr_Completed And ProcessExists($PID_Chi))) ? 1 : 0 which is the same as $F_Akr_Completed = Int(Not ($F_Akr_Completed And ProcessExists($PID_Chi)))
Scala spec unit tests
I ve got the following class and I want to write some Spec test cases, but I am really new to it and I don't know how to start. My class do loke like this:
class Board{
val array = Array.fill(7)(Array.fill(6)(None:Option[Coin]))
def move(x:Int, coin:Coin) {
val y = array(x).indexOf(None)
require(y >= 0)
array(x)(y) = Some(coin)
}
def apply(x: Int, y: Int):Option[Coin] =
if (0 <= x && x < 7 && 0 <= y && y < 6) array(x)(y)
else None
def winner: Option[Coin] = winner(Cross).orElse(winner(Naught))
private def winner(coin:Coin):Option[Coin] = {
val rows = (0 until 6).map(y => (0 until 7).map( x => apply(x,y)))
val cols = (0 until 7).map(x => (0 until 6).map( y => apply(x,y)))
val dia1 = (0 until 4).map(x => (0 until 6).map( y => apply(x+y,y)))
val dia2 = (3 until 7).map(x => (0 until 6).map( y => apply(x-y,y)))
val slice = List.fill(4)(Some(coin))
if((rows ++ cols ++ dia1 ++ dia2).exists(_.containsSlice(slice)))
Some(coin)
else None
}
override def toString = {
val string = new StringBuilder
for(y <- 5 to 0 by -1; x <- 0 to 6){
string.append(apply(x, y).getOrElse("_"))
if (x == 6) string.append ("\n")
else string.append("|")
}
string.append("0 1 2 3 4 5 6\n").toString
}
}
Thank you!
I can only second Daniel's suggestion, because you'll end up with a more practical API by using TDD.
I also think that your application could be nicely tested with a mix of specs2 and ScalaCheck. Here the draft of a Specification to get you started:
import org.specs2._
import org.scalacheck.{Arbitrary, Gen}
class TestSpec extends Specification with ScalaCheck { def is =
"moving a coin in a column moves the coin to the nearest empty slot" ! e1^
"a coin wins if" ^
"a row contains 4 consecutive coins" ! e2^
"a column contains 4 consecutive coins" ! e3^
"a diagonal contains 4 consecutive coins" ! e4^
end
def e1 = check { (b: Board, x: Int, c: Coin) =>
try { b.move(x, c) } catch { case e => () }
// either there was a coin before somewhere in that column
// or there is now after the move
(0 until 6).exists(y => b(x, y).isDefined)
}
def e2 = pending
def e3 = pending
def e4 = pending
/**
* Random data for Coins, x position and Board
*/
implicit def arbitraryCoin: Arbitrary[Coin] = Arbitrary { Gen.oneOf(Cross, Naught) }
implicit def arbitraryXPosition: Arbitrary[Int] = Arbitrary { Gen.choose(0, 6) }
implicit def arbitraryBoardMove: Arbitrary[(Int, Coin)] = Arbitrary {
for {
coin <- arbitraryCoin.arbitrary
x <- arbitraryXPosition.arbitrary
} yield (x, coin)
}
implicit def arbitraryBoard: Arbitrary[Board] = Arbitrary {
for {
moves <- Gen.listOf1(arbitraryBoardMove.arbitrary)
} yield {
val board = new Board
moves.foreach { case (x, coin) =>
try { board.move(x, coin) } catch { case e => () }}
board
}
}
}
object Cross extends Coin {
override def toString = "x"
}
object Naught extends Coin {
override def toString = "o"
}
sealed trait Coin
The e1 property I've implemented is not the real thing because it doesn't really check that we moved the coin to the nearest empty slot, which is what your code and your API suggests. You will also want to change the generated data so that the Boards are generated with an alternation of x and o. That should be a great way to learn how to use ScalaCheck!
I suggest you throw all that code out -- well, save it somewhere, but start from zero using TDD. The Specs2 site has plenty examples of how to write tests, but use TDD -- test driven design -- to do it. Adding tests after the fact is suboptimal, to say the least. So, think of the most simple case you want to handle of the most simple feature, write a test for that, see it fail, write the code to fix it. Refactor if necessary, and repeat for the next most simple case. If you want help with how to do TDD in general, I heartily endorse the videos about TDD available on Clean Coders. At the very least, watch the second part where Bob Martin writes a whole class TDD-style, from design to end. If you know how to do testing in general but are confused about Scala or Specs, please be much more specific about what your questions are.
Regular expression puzzle
This is not homework, but an old exam question. I am curious to see the answer.
We are given an alphabet S={0,1,2,3,4,5,6,7,8,9,+}. Define the language L as the set of strings w from this alphabet such that w is in L if:
a) w is a number such as 42 or w is the (finite) sum of numbers such as 34 + 16 or 34 + 2 + 10
and
b) The number represented by w is divisible by 3.
Write a regular expression (and a DFA) for L.
This should work:
^(?:0|(?:(?:[369]|[147](?:0*(?:\+?(?:0\+)*[369]0*)*\+?(?:0\+)*[147]0*(?:\+?(?:0\
+)*[369]0*)*\+?(?:0\+)*[258])*(?:0*(?:\+?(?:0\+)*[369]0*)*\+?(?:0\+)*[258]|0*(?:
\+?(?:0\+)*[369]0*)*\+?(?:0\+)*[147]0*(?:\+?(?:0\+)*[369]0*)*\+?(?:0\+)*[147])|[
258](?:0*(?:\+?(?:0\+)*[369]0*)*\+?(?:0\+)*[258]0*(?:\+?(?:0\+)*[369]0*)*\+?(?:0
\+)*[147])*(?:0*(?:\+?(?:0\+)*[369]0*)*\+?(?:0\+)*[147]|0*(?:\+?(?:0\+)*[369]0*)
*\+?(?:0\+)*[258]0*(?:\+?(?:0\+)*[369]0*)*\+?(?:0\+)*[258]))0*)+)(?:\+(?:0|(?:(?
:[369]|[147](?:0*(?:\+?(?:0\+)*[369]0*)*\+?(?:0\+)*[147]0*(?:\+?(?:0\+)*[369]0*)
*\+?(?:0\+)*[258])*(?:0*(?:\+?(?:0\+)*[369]0*)*\+?(?:0\+)*[258]|0*(?:\+?(?:0\+)*
[369]0*)*\+?(?:0\+)*[147]0*(?:\+?(?:0\+)*[369]0*)*\+?(?:0\+)*[147])|[258](?:0*(?
:\+?(?:0\+)*[369]0*)*\+?(?:0\+)*[258]0*(?:\+?(?:0\+)*[369]0*)*\+?(?:0\+)*[147])*
(?:0*(?:\+?(?:0\+)*[369]0*)*\+?(?:0\+)*[147]|0*(?:\+?(?:0\+)*[369]0*)*\+?(?:0\+)
*[258]0*(?:\+?(?:0\+)*[369]0*)*\+?(?:0\+)*[258]))0*)+))*$
It works by having three states representing the sum of the digits so far modulo 3. It disallows leading zeros on numbers, and plus signs at the start and end of the string, as well as two consecutive plus signs.
Generation of regular expression and test bed:
a = r'0*(?:\+?(?:0\+)*[369]0*)*\+?(?:0\+)*'
b = r'a[147]'
c = r'a[258]'
r1 = '[369]|[147](?:bc)*(?:c|bb)|[258](?:cb)*(?:b|cc)'
r2 = '(?:0|(?:(?:' + r1 + ')0*)+)'
r3 = '^' + r2 + r'(?:\+' + r2 + ')*$'
r = r3.replace('b', b).replace('c', c).replace('a', a)
print r
# Test on 10000 examples.
import random, re
random.seed(1)
r = re.compile(r)
for _ in range(10000):
x = ''.join(random.choice('0123456789+') for j in range(random.randint(1,50)))
if re.search(r'(?:\+|^)(?:\+|0[0-9])|\+$', x):
valid = False
else:
valid = eval(x) % 3 == 0
result = re.match(r, x) is not None
if result != valid:
print 'Failed for ' + x
Note that my memory of DFA syntax is woefully out of date, so my answer is undoubtedly a little broken. Hopefully this gives you a general idea. I've chosen to ignore + completely. As AmirW states, abc+def and abcdef are the same for divisibility purposes. Accept state is C. A=1,4,7,BB,AC,CA B=2,5,8,AA,BC,CB C=0,3,6,9,AB,BA,CC Notice that the above language uses all 9 possible ABC pairings. It will always end at either A,B,or C, and the fact that every variable use is paired means that each iteration of processing will shorten the string of variables. Example: 1490 = AACC = BCC = BC = B (Fail) 1491 = AACA = BCA = BA = C (Success)
Not a full solution, just an idea: (B) alone: The "plus" signs don't matter here. abc + def is the same as abcdef for the sake of divisibility by 3. For the latter case, there is a regexp here: http://blog.vkistudios.com/index.cfm/2008/12/30/Regular-Expression-to-determine-if-a-base-10-number-is-divisible-by-3 to combine this with requirement (A), we can take the solution of (B) and modify it: First read character must be in 0..9 (not a plus) Input must not end with a plus, so: Duplicate each state (will use S for the original state and S' for the duplicate to distinguish between them). If we're in state S and we read a plus we'll move to S'. When reading a number we'll go to the new state as if we were in S. S' states cannot accept (another) plus. Also, S' is not "accept state" even if S is. (because input must not end with a plus).